This proposal tests the hypothesis that naturally-occurring and synthetic organoselenium compounds (SeC) modify growth of human prostate cancer (CaP) cells by targeting redox sensitive signal proteins and transcription factors thereby regulating proliferative and/or apoptotic responses. Inhibition of cell proliferation and induction of apoptosis are major cancer preventive activities of SeC. Preliminary studies document selective growth inhibitory effects of SeCs utilizing phenotypically similar androgen-responsive (AR+) and - non-responsive (AR-) human LNCaP cells. Proteomic studies reveal that the form of Se and the cell's hormonal status play critical roles in growth inhibition. To test our hypothesis we formulated 3 specific aims. Aim 1 characterizes antiproliferative mechanisms of SeC in AR+ and AR- cells. Studies will compare time and dose-response effects of SeC on cytometric measurements, cell proliferation, apoptotic_processes, and intracellular redox environment. Proteomic analyses will examine expression profiles of selected redox sensitive signal and transcription factors. Aim 2 identifies sites and characterizes the type of interaction between SeC and selected redox signal proteins. Purified or recombinant proteins selected from prolifiterative and apoptotic pathways will be studied to identify occurrences of covalent intra- and intermolecular -S-S- or S- Se conjugates. Immunoprecipitations of similar signal proteins from control and SeC-treated AR+ and AR- cells will be studied. HPLC separation of proteolytic digests followed by MALDI-TOF MS analyses will locate sites of protein modification. In Aim 3, nude mice implanted with AR+ and AR- cells and TRAMP mice are fed diets containing low and high levels of SeC (including selenized yeast). Global expression profiles of redox-sensitive signal proteins as defined in Aim 1 will be determined relative to dietary SeC in these models. Completion of this study will define the molecular targets of SeC at the proteomic level and will identify in AR+ and AR- human prostate cancer cells distinct physiological responses necessary for chemopreventive action. Also, this study aims to determine whether the molecular environment in which Se resides mediates redox sensitive signal and/or transcription factors that regulate proliferative and/or apoptotic processes in CaP. Molecular targets identified in this study will provide relevant biomarkers useful for the on-going SELECT Study that examines selenomethionine for prevention of CaP. Our proposal determines the role of various forms of selenium (natural and synthetic) on protein targets implicated in development of human prostate cancer. The long-term goal of our reseach is to design appropriate dietary strategies for prevention of prostate cancer.